Squalene synthetase is a microsomal enzyme which catalyzes the reductive dimerization of two molecules of farnesyl pyrophosphate (FPP) in the presence of nicotinamide adenine dinucleotide phosphate (reduced form) (NADPH) to form squalene (Poulter, C.D.; Rilling, H.C., in "Biosynthesis of Isoprenoid Compounds", Vol. I, Chapter 8, pp. 413-441, J. Wiley and Sons, 1981, and references therein). This enzyme is the first committed step of the de novo cholesterol biosynthetic pathway. The selective inhibition of this step should allow the essential pathways to isopentenyl tRNA, ubiquinone, and dolichol to proceed unimpeded. Squalene synthetase along with HMG-CoA reductase have been shown to be down-regulated by receptor mediated LDL uptake (Faust, J.R.; Goldstein, J.L.; Brown, M.S. Proc. Nat. Acad. Sci. U.S.A. 1979, 76, 5018-5022), lending credence to the proposal that inhibiting squalene synthetase will lead to an up-regulation of LDL receptor levels, as has been demonstrated for HMG-CoA reductase, and thus ultimately should be useful for the treatment and prevention of hypercholesterolemia and atherosclerosis.
European Patent Publication 0356866A2 discloses phosphorus-containing compounds which inhibit the enzyme squalene synthetase and thus are useful as hypocholesterolemic agents and have the following structure ##STR2## wherein Q is ##STR3## or a bond:
n is 1, 2, 3 or 4;
X is --O--, --NH--, or --NR.sup.4 ;
R, R.sup.1 and R.sup.1a may be the same or different and are H, lower alkyl, lower alkenyl or a metal ion;
R.sup.2 and R.sup.3 may be the same or different and are H or halogen;
R.sup.4 is lower alkyl;
with the proviso that when X is 0, n is 2, 3 or 4.
European Patent Publication 0409181A3 discloses phosphorus-containing compounds which are inhibitors of cholesterol biosynthesis (by inhibiting de novo squalene biosynthesis), and thus are useful as hypocholesterolemic agents and antiatherosclerotic agents, which have the structure ##STR4## wherein m is 1, 2 or 3; n is 0, 1, 2, or 3;
Y.sup.1 and Y.sup.2 are H or halogen;
R.sup.2, R.sup.3 and R.sup.4 may be the same or different and are independently H, metal ion, C.sub.1 to C.sub.8 alkyl or C.sub.3 to C.sub.12 alkenyl;
X is O, S, NH or NCH.sub.2 R.sup.15 wherein R.sup.15 is H or C.sub.1 to C.sub.5 alkyl; and
R.sup.1 is R.sup.5 --Q.sup.1 --Q.sup.2 --Q.sup.3 -- wherein Q.sup.1, Q.sup.2 and Q.sup.3 are the same or different and are independently ##STR5## a single bond, with the proviso that if Q.sup.1 is a bond, then Q.sup.2 and Q.sup.3 are bonds and if Q.sup.2 is a bond, then Q.sup.3 is a bond, and wherein R.sup.6 is H, alkyl, halo, or haloalkyl; R.sup.7 is H, halo, alkyl or alkylthio; R.sup.8 is H, halogen, trimethylsilyl or lower alkyl; R.sup.9 is H or lower alkyl-; ##STR6## R.sup.16 --C.tbd.C--CH.sub.2 -- (wherein R.sup.16 is H or lower alkyl) or CH.sub.3 (CH.sub.2)p where p is an integer from 2 to 7; R.sup.10, and R.sup.11 are the same or different and are independently H, lower alkyl, halogen, haloalkyl or lower alkenyl or R.sup.10 and R.sup.11 can be taken together to form (CH.sub.2)s where s is an integer from 2 to 7; and R.sup.13 and R.sup.14 are the same or different and are independently lower alkyl, with the proviso that if all of Q.sup.1, Q.sup.2 and Q.sup.3 are bonds, then both R.sup.10 and R.sup.11 cannot be H and R.sup.5 cannot be alkyl(CH.sub.2)p-- with p.ltoreq.4; including all stereoisomers thereof.
U.S. Pat. No. 4,871,721 to Biller et al disclose phosphorus-containing compounds which inhibit the enzyme squalene synthetase and thus are useful as hypocholesterolemic agents and have the following structure ##STR7## wherein Q is ##STR8## or a bond;
Z is --(CH.sub.2).sub.n -- or --(CH.sub.2).sub.p --CH=CH--(CH.sub.2).sub.m --, wherein n is 1 to 5; p is 0, 1 or 2; m is 0, 1 or 2;
R, R.sup.1 and R.sup.1a may be the same or different and are H, lower alkyl or a metal ion; and
R.sup.2 and R.sup.3 may be the same or different and are H or halogen.
European Patent Publication 0298555A1 discloses bone active methylene phosphonoalkylphosphinic acids, and the pharmaceutically-acceptable salts and esters thereof, having the general structure ##STR9## wherein the A, B, and R moieties are as defined in the EP.